1. Field of the Invention
The present invention relates to a pyroelectric sensing device, and more particularly, to a pyroelectric sensing device for driving pyroelectric sensors to shift.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is an illustrative diagram of a pyroelectric sensing device according to prior art. The pyroelectric sensing device 1 is an infrared sensing device which detects whether any human exists in the environment through detecting the infrared radiation emitted by the human body. As shown in FIG. 1, the pyroelectric sensing device 1 comprises two pyroelectric sensors 10, and the two pyroelectric sensors 10 are connected in series wherein the positive electrode of one pyroelectric sensor 10 is connected to the negative electrode of the other pyroelectric sensor 10. The two pyroelectric sensors 10 detect the infrared radiation emitted due to the environment temperature, and convert the detected infrared radiation into a voltage data. When the environment temperature varies, the voltage data converted by the two pyroelectric sensors 10 are offset so that an output voltage is zero. When a human enters the environment where the pyroelectric sensing device 1 is disposed, since the two pyroelectric sensors 10 do not generate the same output voltage, the pyroelectric sensing device 1 is temporarily in a unbalanced status or state, and thus generates a non-zero output voltage.
Because the pyroelectric sensing device 1 is cheap and simple in circuit design, the pyroelectric sensing device 1 is broadly used when human body detecting is required, such as in the application of burglarproof/anti-theft systems, automatic light switching control detection and so on. The disadvantage of the conventional pyroelectric sensing device 1, however, is that the output voltage is generated only when the infrared radiation sensed by the two pyroelectric sensors 10 are different. Generally speaking, the pyroelectric sensing device 1 is motionlessly disposed in the environment, and is only able to detect a moving human body. When the human body is motionless, the pyroelectric sensing device 1 is not able to detect the (motionless) human body, and thus the application of the pyroelectric sensing device 1 is limited.